1. Field of the Invention
The present invention relates to a semiconductor device using a gate dielectric film including Hf (hafnium) and to a method for manufacturing the semiconductor device.
2. Description of the Related Art
With advance in the scale-down of a MOS transistor, a leakage current of a SiO2 gate dielectric film and depletion of a polycrystalline silicon gate electrode become a big problem. The following technique has been proposed as one means for solving the foregoing problem. According to the technique, one of a high dielectric constant gate dielectric film, that is, gate dielectric film including Hf (Hf gate dielectric film) and a metal silicide gate electrode are combined.
The following method has been known to control a threshold voltage of a MOS transistor including a metal silicide gate electrode. According to the foregoing method, impurities such as boron, phosphorus and antimony are implanted into the metal silicide gate electrode.
However, in the case where the Hf gate dielectric film and the metal silicide gate electrode are combined, there is the following problem. Even if impurity is implanted into the metal silicide gate electrode, it is difficult to control the threshold voltage due to so-called Fermi level pinning phenomenon. In particular, in the case of p-channel MOS transistor, as the threshold voltage shifts largely to negative side in addition to inversion capacitance becomes small, the problem that desired drain current is not secured occurs (T. Aoyama, et al., Proc. IWGI 174 (2003)).
In the case where aluminum (metal) is implanted into the metal silicide gate electrode, and then, heat treatment is carried out to form an aluminum film between the metal silicide gate elected and the Hf gate dielectric film, a magnitude (|Vthn|) of a threshold voltage (Vthn) of an n-channel MOS transistor is made small (Y. H. Kim et al., Systematic Study of Work function Engineering and Scavenging Effect Using NiSi alloy FUSI Metal Gate with Advanced Gate Stacks, 2005 IEEE).
However, according to the foregoing method, a magnitude (|Vthp|) of a threshold voltage (Vthp) of a p-channel MOS transistor is no made small.
That is, in the case where the Hf gate dielectric film and the metal silicide gate electrode are combined, it is difficult to make small both |Vthn| and |Vthn| according to the conventional method.